[llvm] [UniformityAnalysis] Replace DenseMap with SmallVector indexed by block number. NFC (PR #210564)

[Alexis Engelke via llvm-commits]

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@@ -104,30 +104,37 @@ template <typename ContextT> class ModifiedPostOrder {
   void clear() { Order.clear(); }
   void compute(const CycleInfoT &CI);
 
-  unsigned count(BlockT *BB) const { return POIndex.count(BB); }
+  unsigned count(BlockT *BB) const {
+    unsigned Num = GraphTraits<BlockT *>::getNumber(BB);
+    return Num < POIndex.size() && POIndex[Num] != InvalidIndex;
+  }
   const BlockT *operator[](size_t Idx) const { return Order[Idx]; }
 
   void appendBlock(const BlockT &BB, bool IsReducibleCycleHeader = false) {
-    POIndex[&BB] = Order.size();
+    unsigned Num = GraphTraits<const BlockT *>::getNumber(&BB);
+    POIndex[Num] = Order.size();
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aengelke wrote:

Is this always safe without a bounds check?

https://github.com/llvm/llvm-project/pull/210564